We are completing a world-wide population genetic survey of Aedes aegypti populations. We will soon have over 40 populations analyzed for 23 gene-enzyme loci by electrophoretic techniques. Simulations of outdoor versus indoor enviornments of A. aegypti have been established in the laboratory with the purpose of detecting what factors are responsible for the genetic distinctness of these sympatric forms. Using electrophoretic techniques, we are studying the distributions of Culex pipiens subspecies in the U.S., especially looking for zones of hybridization and/or introgression.